1. Field of the Invention
The present invention relates to a fluid filled-type vibration isolation apparatus which absorbs vibration form a vibration generating portion such as an engine.
2. Description of the Related Art
A vibration isolation apparatus is disposed as an engine mount between an engine and a vehicle body in the vehicle engine room. The vibration isolation apparatus inhibits transmission of vibration from the engine to the vehicle body. The engine vibrates in various modes of vibration. For example, shake vibration has a frequency of less than 15 Hz. Idle vibration has a frequency range in the vicinity of 20 to 40 Hz. High-frequency vibration has a frequency of greater than or equal to 80 Hz. A fluid filled-type vibration isolation apparatus having a plurality of fluid chambers is disclosed in Japanese Patent Application Laid-Open Nos. 2-42226 and 2-42227 as a vibration isolation apparatus which absorbs vibrations of a wide range of frequencies such as those listed above.
This vibration isolation apparatus has three fluid chambers layered one after another and disposed at one side of an inner cylinder. A communication path, i.e., a restricted path, is disposed on the other side of the inner cylinder to communicate the fluid chambers with each other. Therefore, the complex internal structure of the apparatus complicates assembling. To effectively absorb idle vibration from the engine, it is necessary to increase flow resistance and resonance of the fluid which are both caused when the fluid flows through the communication path. Thus, the communication path should be extended in order top increase the flow resistance and resonance of the fluid. In this vibration isolation apparatus, however, the fluid chambers should be provided so as not to interfere with each other. Therefore, it is impossible to extend the length of the communication path. As a result, flow resistance and resonance of the fluid cannot be increased much more. Of course, the communication path can be lengthened by separately mounting an other member to form the communication path. Such an extension, however, results in an even more complex structure and difficult assembly of the vibration isolation apparatus.